Semiconductor laser device

ABSTRACT

This semiconductor laser device comprises a semiconductor laser element  10 , which is provided with a Cr layer  13  and an Au layer  14 , a silicon submount  20 , which is provided with a Cr layer  22  and an Au layer  23 , and a metal base  30 . The surface of the semiconductor laser element  10  on which the Au layer  14  is provided and the surface of the silicon submount  20  on which the Au layer  23  is provided are directly joined together.

TECHNICAL FIELD

The present invention relates to a semiconductor laser device, andparticularly to the construction of a semiconductor laser device forradiating heat from an active layer.

BACKGROUND ART

FIG. 4 is a longitudinal sectional view of a conventional semiconductorlaser device. Reference numeral 10 is a semiconductor laser element,reference numeral 11 is an LD (laser diode), reference numeral 12 is anactive layer, reference numeral 13 is a Cr layer, reference numeral 14is an Au layer, reference numeral 15 is an Au layer, reference numeral16 is an Au—Ge layer, reference numeral 17 is an Au layer, referencenumeral 30 is a metal base, reference numeral 31 is a metal block, andreference numeral 40 is a conductive adhesive. In order to radiate theheat that is generated in the active layer 12, the semiconductor laserelement 10 is attached to the metal base 30 by the conductive adhesive40. The metal base 30 functions as a heat sink.

FIG. 5 is a longitudinal sectional view of a different semiconductorlaser device. This device is disclosed in Japanese Patent ApplicationLaid-open No. S59-31085. In this device, in order to radiate the heatgenerated from a light 12 shown in FIG. 4, a silicon submount 20 isinserted between the semiconductor laser element 10 and the metal base30, and each of these are constituted by brazing with a gold and siliconbrazing material 50 and 60. Note that the silicon submount 20 is madefrom a heat sink with a thermal expansion coefficient close to thematerial constituting the semiconductor laser element.

DISCLOSURE OF THE INVENTION

However, the semiconductor laser device shown in FIG. 4 has problemsassociated with it, such as the conductive adhesive 40 entering theresonator surface of the active layer 12, or adhering thereto duringattachment, and this contaminates the resonator surface and produces adefective product. The problem also arises that a sufficient radiationeffect cannot be obtained due to voids being produced inside theconductive adhesive 40.

Further, there are also problems with the semiconductor laser deviceshown in FIG. 5, in that the resonator surface of the active layer 12becomes contaminated due to brazing material 50 surrounding and enteringthe resonator surface, creating the possibility of producing a defectiveproduct.

Therefore, an object of the present invention is to provide asemiconductor laser device that is able to effectively radiate heatgenerated in the active layer, without contaminating the resonatorsurface of the semiconductor laser element.

In order to solve the above-mentioned problems, the semiconductor laserdevice according to the present invention comprises: a heat sinkinterposed between a semiconductor laser element having an active layer,and a metal base, wherein a metallic layer and an Au layer are providedon whichever of the front or back surfaces of the semiconductor laserelement is closer to the active layer; a metallic layer and an Au layerare provided on the surface of the heat sink on the semiconductor laserelement side; and the Au layer that is provided on the semiconductorlaser element and the Au layer that is provided on the heat sink arejoined together. Note that it is desirable that the base and the heatsink are attached by a conductive adhesive or joined using a metalliclayer and an Au layer in a similar way to the above.

More specifically, this semiconductor laser device is constituted bycomprising: a semiconductor laser element; a metal base; and a heat sinkinterposed between the semiconductor laser element and the metal base,wherein a first metallic layer to increase the adhesiveness of the goldand the semiconductor laser element, and a first Au layer on the uppersurface thereof are provided on the surface of the semiconductor laserelement on which the active layer is formed. A second metallic layer toincrease the adhesiveness of the gold and the heat sink and preventeutectic bonding, and a second Au layer on the upper surface thereof areprovided on the heat sink. The surface of the semiconductor laserelement on which the first Au layer is provided and the surface of theheat sink on which the second Au layer is provided are directly joined,and the surface of the heat sink opposing the surface to which thesemiconductor laser element is directly joined is attached to the metalbase with the conductive adhesive.

In this way, since the semiconductor laser element and the heat sink aredirectly joined, the resonator surface of the semiconductor laser doesnot become contaminated. Further, since the resonator surface does notbecome contaminated, the surface of the semiconductor laser element onwhich the active layer is formed and the heat sink can be directlyjoined. Accordingly, since the semiconductor laser element and the heatsink are joined with good adhesiveness, the heat from the active layercan be effectively radiated directly to the silicon submount.

Further, the semiconductor laser device according to the presentinvention is constituted by comprising: a semiconductor laser element; ametal base; and a heat sink interposed between the semiconductor laserelement and the metal base, wherein a first metallic layer to increasethe adhesiveness of the gold and the semiconductor laser element, and afirst Au layer on the upper surface thereof are provided on the surfaceof the semiconductor laser element on which the active layer is formed.A second metallic layer to increase the adhesiveness of the gold and theheat sink and prevent eutectic bonding, and a second Au layer on theupper surface thereof are provided on the heat sink. A third metalliclayer to increase the adhesiveness of the gold and the metal base, and athird Au layer on the upper surface thereof are provided on the metalbase. The surface of the semiconductor laser element on which the firstAu layer is provided and one side of the heat sink on which the secondAu layer is provided, and the other side of the heat sink on which thesecond Au layer is provided and the surface of the metal base on whichthe third Au layer is provided are each in contact and directly joinedto each other.

In this way, since the semiconductor laser element, the heat sink andthe metal base are directly joined, the semiconductor laser device canbe made at one time, improving labor efficiency. Further, since thesemiconductor laser element and the heat sink are directly joined, theresonator surface of the semiconductor laser does not becomecontaminated. Further, since the resonator surface does not becomecontaminated, the surface of the semiconductor laser element on whichthe active layer is formed and the heat sink can be directly joined.Accordingly, since the semiconductor laser element and the heat sink arejoined with good adhesiveness, the heat from the active layer can beeffectively radiated directly to the silicon submount.

Further, the semiconductor laser device according to the presentinvention may have a heat sink made of silicon, and the second metalliclayer may function to prevent eutectic bonding of the gold and thesilicon. Silicon has a similar thermal expansion coefficient to acompound semiconductor made from GaAs or the like, which forms thesemiconductor laser element. Therefore by making the heat sink fromsilicon, heat from the active layer can be effectively dispersed andradiated. Further, since a second metallic layer is inserted between thesecond Au layer and the heat sink made of silicon in order to preventthe eutectic bonding of the gold and the silicon, this can prevent theformation of brazing materials due to eutectic bonding of the second Aulayer and the silicon heat sink, thereby preventing contamination of theactive layer's resonator surface due to gold and silicon brazingmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a semiconductor laser device according tothe first embodiment;

FIG. 2 is a sectional view of a semiconductor laser device according tothe second embodiment;

FIG. 3 is a graph comparing the temperature rise when a semiconductorlaser device according to the first embodiment is operated, compared toa conventional semiconductor laser device;

FIG. 4 is a sectional view of a conventional semiconductor laser device;and

FIG. 5 is a sectional view of a conventional semiconductor laser device.

BEST MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the accompanying drawings. The same reference numerals areused to indicate the same elements and repetitive explanations areomitted.

FIG. 1 shows a sectional view of a semiconductor laser device accordingto the first embodiment. A semiconductor laser device according to thefirst embodiment comprises a semiconductor laser element 10, a siliconsubmount 20, and a metal base 30.

The semiconductor laser element 10 has a laser diode (LD) 11 containingan active layer 12 made of GaAs, a Cr (metallic) layer 13 with a filmthickness of 10 to 30 nm, an electrode made of an Au layer 14 with afilm thickness of 300 to 1000 nm, an Au layer 15 with a film thicknessof 10 nm, an Au—Ge layer 16 with a film thickness of 250 nm, and anelectrode made of an Au layer 17 with a film thickness of 750 nm.

The silicon submount 20 has a p-type silicon layer 21 as a heat sink, aCr (metallic) layer 22 with a film thickness of 10 to 30 nm, and an Aulayer 23 with a film thickness of 300 to 1000 nm. The metal base 30 hasa metal block 31 made of Cu.

The Au layer 14 of the semiconductor laser element 10 and the Au layer23 of the silicon submount 20 are directly joined, and the Au layer 23of the silicon submount 20 and the metal block 31 of the metal base 30are attached by a conductive adhesive 40 made of copper solder, and thesemiconductor laser device according to the first embodiment is therebyconstituted.

According to the construction of the semiconductor laser device of thefirst embodiment shown in FIG. 1, since the semiconductor laser element10 and the silicon submount 20 are directly joined, the resonatorsurface of the active layer 12 does not become contaminated, and it isdifficult to produce a defective product, so a good yield can beproduced. Note that with regard to the active layer 12, the longitudinaldirection of the resonator is at right angles to the thickness directionof the semiconductor laser element 10, and laser light is outputted fromthe end surface (resonator surface) in the longitudinal direction.

In the semiconductor laser device according to the present embodiment,since the resonator surface of the active layer 12 does not becomecontaminated, the surface of the semiconductor laser 10 on which theactive layer 12 is formed, can be directly joined to the siliconsubmount 20. Accordingly the semiconductor laser element 10 and thesilicon submount 20 are joined together with good adhesiveness, and theheat from the active layer 12 is effectively radiated directly to thesilicon submount 20.

In addition, since the Cr layer 22 is inserted between the Au layer 23and the silicon (Si) layer 21 in order to prevent eutectic bonding ofthe gold and the silicon, formation of brazing material due to eutecticbonding of the Au layer 23 and the silicon layer 21 can be prevented,thereby preventing contamination of the resonator surface of the activelayer 12 due to gold and silicon brazing material. Further, by providingthe Cr layer 13 and the Cr layer 22, peeling of the Au layer 14 and theAu layer 23 can be prevented.

FIG. 2 is a sectional view of a semiconductor laser device according tothe second embodiment.

The semiconductor laser device according to this embodiment comprises asemiconductor laser element 10, a silicon submount 20, and a metal base30.

The semiconductor laser element 10 has an LD 11 containing an activelayer 12 made of GaAs, a Cr (metallic) layer 13 with a film thickness of10 to 30 nm, an electrode made of an Au layer 14 with a film thicknessof 300 to 1000 nm, an Au layer 15 with a film thickness of 10 nm, anAu—Ge layer 16 with a film thickness of 250 nm, and an electrode made ofan Au layer 17 with a film thickness of 750 nm.

The silicon submount 20 has a P-type silicon layer 21 as a heat sink, aCr (metallic) layer 22 with a film thickness of 10 to 30 nm, and an Aulayer 23 with a film thickness of 300 to 1000 nm. The metal base 30 hasa metal block 31 made of Cu, a Cr (metallic) layer 32, and an Au layer33.

The Au layer 14 of the semiconductor laser element 10, the Au layer 23of the silicon submount 20, the surface opposing the Au layer 14 of thesemiconductor laser element 10, the Au layer 23 of the silicon submount20 provided on the opposite side, and the Au layer 33 of the metal base30 are simultaneously directly joined, and the semiconductor laserdevice of the second embodiment is thereby constituted.

More specifically, the thickness of the metallic layer 13, the metalliclayer 22 and/or the metallic layer 32 is at least 10 nm and no more than30 nm. If the thickness of the metallic layers 13 and 22 is less thanthe above-mentioned lower limit, the adhesive force declines, and if itis greater than the above-mentioned upper limit the manufacturing costincreases.

Further, the thickness of the Au layer 14, the Au layer 23 and/or the Aulayer 33 is at least 300 nm and not more than 1000 nm. If the thicknessof the Au layers 14, 23, and 33 is less than the above-mentioned lowerlimit, the adhesive force declines, and if it is greater than theabove-mentioned upper limit, manufacturing cost is increased.

According to the construction of the semiconductor laser device of thesecond embodiment shown in FIG. 2, since the semiconductor laser element10, the silicon submount 20 and the metal base 30 are directly joined,the semiconductor laser device can be made at one time, and laborefficiency can be improved. Further, since the semiconductor laserelement 10 and the silicon submount 20 are directly joined, theresonator surface of the active layer 12 does not become contaminated,and it is difficult to produce a defective product, so a good yield canbe produced.

Further, since the resonator surface of the active layer 12 does notbecome contaminated, the surface of the semiconductor laser 10 on whichthe active layer 12 is formed and the silicon submount 20 can bedirectly joined. Accordingly, since the semiconductor laser element 10and the silicon submount 20 are joined together with good adhesiveness,the heat from the active layer 12 is directly and effectively radiatedto the silicon submount 20.

In addition, since the Cr layer 22 is inserted between the Au layer 23and the silicon layer 21 in order to prevent eutectic bonding of thegold and the silicon, formation of brazing material due to eutecticbonding of the Au layer 23 and the silicon layer 21 can be prevented,thereby preventing contamination of the resonator surface of the activelayer 12 due to gold and silicon brazing material. Further, by providingthe Cr layer 13 and the Cr layer 22, peeling of the Au layer 14 and theAu layer 23 can be prevented.

Next, a graph is shown in FIG. 3 of the temperature rise of thesemiconductor laser element 10 in the semiconductor laser deviceaccording to the first embodiment shown in FIG. 1, and the conventionalsemiconductor laser device shown in FIG. 4, when an electric current isincreased from 10A to 30A and the device is operated. The graph alsoshows the rise in temperature when the area of the silicon submount 20in the semiconductor laser device in FIG. 1 is changed.

As can be seen from FIG. 3, in comparison to the conventionalsemiconductor laser device shown in FIG. 4 that is not provided with asilicon submount 20, in the semiconductor laser device of the firstembodiment shown in FIG. 1 that is provided with the silicon submount20, the temperature rise of the semiconductor element 10 is hugelyreduced. It was possible to reduce the temperature rise by approximately60% with a CW-laser and approximately 90% with a Q-CW-laser. Further, bymaking the area of the silicon submount 20 larger, it can be seen thatthe temperature rise can be further reduced.

Note that the first and second embodiments are not limited to the above.The material for the LD 11 is not limited to GaAs, and maybe InGaAs oranother compound semiconductor. Further, a silicon layer 21 is used forthe heat sink, but a material such as diamond, which has a thermalexpansion coefficient similar to the LD 11 may also be used for the heatsink. Further, Cu is used as an example of a material for the metalblock 31, but any material can be used, such as CuW, Kovar metal or SiC,as long as it has a good thermal conductivity. Further, copper solder isused as an example of the conductive adhesive 40, however otherconductive adhesives may also be used, such as silver paste orlead-copper.

In addition, Cr is used as an example of a metal to prevent eutecticbonding of the gold (Au) and silicon (Si) and increase adhesiveness ofthe Au layer, however other materials may be used instead of Cr, such asTi, Pt, or Mo, as long as the material can prevent eutectic bonding ofthe gold and the silicon, and adheres sufficiently to the LD 11, siliconlayer 21, metal block 31 and Au layer. Further, the type of metalliclayer provided on the LD 11, silicon layer 21 and metal block 31 doesnot have to be the same. Note that if the heat sink is made of amaterial other than silicon (Si), the type of metallic material thatwill prevent eutectic bonding of the gold and the heat sink, andincrease the adhesiveness of the Au layer will obviously be different.

As described in detail above, with respect to the semiconductor laserdevice, since the semiconductor laser element and the heat sink aredirectly joined, the resonator surface of the active layer of thesemiconductor laser element does not become contaminated and it isdifficult to produce a defective product, so a good yield is produced.Further, since the resonator surface of the active layer does not becomecontaminated, the surface of the semiconductor laser element on whichthe active layer is formed and the silicon submount can be directlyjoined, thereby joining the semiconductor laser element and the heatsink with good adhesiveness. Thus, the heat from the active layer can bedirectly and effectively radiated to the heat sink.

In addition, since a metallic layer is inserted between the Au layer andthe heat sink in order to prevent eutectic bonding of the gold and theheat sink material and increase the adhesiveness of the Au layer,formation of brazing material due to eutectic bonding of the Au layerand the heat sink material can be prevented, thereby preventingcontamination of the resonator surface of the active layer due tobrazing material formed from the gold and heat sink material.

Accordingly, the temperature rise of the active layer of thesemiconductor laser element can be kept down and deterioration in theproperties of the semiconductor laser can be prevented. Further, sinceit is possible to directly join an optical element consisting of acompound semiconductor such as GaAs with silicon, an optoelectronicintegrated circuit (OEIC) can be achieved.

INDUSTRIAL APPLICABILITY

The present invention can be used in a semiconductor laser device.

1. A semiconductor laser device comprising a heat sink interposedbetween a semiconductor laser element having an active layer and a metalbase, wherein a metallic layer and an Au layer are provided on the frontor back surfaces of the semiconductor laser element whichever is closerto the active layer; a second metallic layer and an second Au layer areprovided on the surface of said heat sink on said semiconductor laserelement side; and said Au layer that is provided on the semiconductorlaser element and said second Au layer that is provided on said heatsink are directly joined together.
 2. The semiconductor laser deviceaccording to claim 1, wherein said base and said heat sink are attachedby a conductive adhesive.
 3. The semiconductor laser device according toclaim 1, wherein a metallic layer and an Au layer are provided on saidbase; a different metallic layer and Au layer are provided on said heatsink; and said Au layer that is provided on said base and said differentAu layer that is provided on said heat sink are joined together.
 4. Thesemiconductor laser device according to claim 1, wherein said heat sinkis made of Si, and one of said metallic layers contains a materialselected from the group consisting of Cr, Ti, Pt and Mo.
 5. Thesemiconductor laser device according to claim 4, wherein the filmthickness of said metallic layer is at least 10 nm.
 6. The semiconductorlaser device according to claim 5, wherein the film thickness of saidmetallic layer is no more than 30 mm.
 7. The semiconductor laser deviceaccording to claim 6, wherein the film thickness of one of said Aulayers is at least 300 nm.
 8. The semiconductor laser device accordingto claim 7, wherein the film thickness of one of said Au layers is nomore than 1000 nm.